nas: fix several sign related issues in signal strength/info reporting
nas: fix several sign related issues in signal strength/info reporting

So, what a nightmare.

In the deprecated "Get Signal Strength" message:
 * Signal strength given as signed integer in 1 dBm units.
 * RSSI given as an unsigned integer in (-1) dBm units.

While in the new "Get Signal Info" message:
 * RSSI given as a signed integer in 1 dBm units.

Then, these seem to be represented in the same way in both messages:
 * ECIO given as an unsigned integer in (-0.5) dBm units.
 * IO given as a signed integer in 1 dBm units.
 * RSRQ given as a signed integer in 1 dBm units.
 * LTE SNR given as a signed integer in (0.1 dB) units.
 * LTE RSRP given as a signed integer in 1 dBm units.

roland-wilhelm/libqmi,roland-wilhelm/libqmi,roland-wilhelm/libqmi,roland-wilhelm/libqmi